The present invention relates to diaphragm control valves and, in particular, it concerns such a valve with a roll diaphragm that deforms equally in two directions.
A large number of diaphragm control valves have been developed and are available from a variety of manufacturers, such as Bermad, Evron, Israel. In general, these valves comprise an upstream side into which flows a fluid from a fluid source, and a downstream side from which fluid can exit for end use, such as irrigation apparatus, for example. In between the upstream and downstream sides of the valve is a valve seat, against which a valve plug can be sealingly seated. The valve plug slides into and out of a plug housing, and a diaphragm is secured to the valve plug which seals the control chamber from the downstream sides of the valve. The control chamber is fitted with a control port through which the fluid pressure in the control chamber is regulated. By controlling the fluid pressure in the control chamber, the valve plug can be forced against the valve seat to shut off flow of fluid from the upstream side to the downstream side, or the valve plug can be lifted from the valve seat to permit flow of fluid from the upstream side to the downstream side. Regulation of the fluid flow is accomplished by adjusting the fluid pressure in the control chamber so as to maintain the position of the plug in a position between fully open and fully closed.
The range of displacement of the valve plug is directly related to the displacement properties of the diaphragm. That is, the valve plug can move only as much as the diaphragm will allow. The larger the diaphragm, the greater the displacement of the valve plug and therefore the larger the opening through which fluid may flow. In valves of the this type using substantially planar or flat diaphragms that are deformed under pressure so as to be displaced between the open and closed positions, the ratio of valve plug displacement to physical diameter of the diaphragm is relatively small, such that the size of a diaphragm necessary for use is a problem for any size pipe, and becomes particularly impractical with larger pipes, for example.
To overcome the problem of physical diameter, the art has turned to the use of what is known in the art as roll diaphragms. Diaphragms of this type are more compact in that they form substantially a sleeve around the valve plug. A problem encountered with this type of diaphragm is that they are particularly effective in actuating a valve plug in only one direction. Due to the amount of diaphragm material used to form the sleeve, when pressure is applied so as to change the direction of valve plug displacement, the unpredictable shapes into which the roll diaphragm may change, as it turns back on itself, can possibly hinder the movement of other parts of the control valve. As a result, the valve plug must be mechanically biased in one direction (usually closed). There is therefore a need for a diaphragm control valve with a non-planar diaphragm that affects bi-directional displacement of a valve plug by way of fluid pressure.